1) Field of the Invention
The present invention relates to the forming of structural members and, more particularly, to the forming of structural members in conjunction with friction stir processing.
2) Description of Related Art
The forming of structural members to desired shapes can be accomplished by forging, stamping, bending, machining, and the like. For example, a preform or blank comprising a flat sheet of metal such as steel, aluminum, titanium, or alloys thereof can be heated in a forge and hammered to the desired shape of the member. Alternatively, a mechanical or hydraulic press can be used to stamp or forge the structural member to the desired shape, e.g., between two opposing dies that define forming surfaces that correspond to the desired contour of the member. Such forming methods are typically quicker and less expensive than casting molten material in the desired shape, and complex shapes can be imparted to the member, such as curves, angles, and the like. However, depending on the particular material of the preform, cracks or weakened portions may result from excessive forming, e.g., the formation of sharp angles or other significant deformations. Therefore, the formation of a particular complex structural member may require that multiple elementary members are formed and then joined by welding or other joining methods. Further, subsequent material processing, e.g., heat treatments such as solution heat treating, aging, and quenching, may be required to achieve desired properties in the formed member. These additional operations add to the manufacturing time and cost of the structural members.
The structural members can also be treated before being formed to the desired shape. For example, according to one proposed method, a preform is supported in a flat configuration, and a friction stir welding tool is inserted into the preform and rotated to plasticize the material of the preform. The friction stir-welding tool is then moved continuously over the surface of the preform so that part of the preform is friction stir processed. The preform is then formed, for example, by forging, stamping, bending, or the like, to the desired shape of the member. Such friction stir processing refines the granular structure of the preform, improving the material properties of the structural member. However, this process is also time-consuming and adds to the cost of the structural member.
Thus, there exists a need for an improved apparatus and process for forming structural members. The process should be capable of forming various configurations of structural members, including those with complex geometric configurations. Further, the process should result in structural members having desired material properties.